Varicella zoster virus (VZV), a human alphaherpesvirus, causes varicella and herpes zoster, and has a significant impact on public health. We will pursue new opportunities to understand molecular mechanisms of VZV pathogenesis using VZV cosmids to construct VZV mutants and SCID mouse models with skin, T cell and dorsal root ganglia (DRG) xenografts. Varicella vaccines (vOka) are effective in healthy children but retain capacities to cause viremia and latency. Our goal is to use VZV cosmids and the SCIDhu skin, T cell and neural models to define options for an improved varicella vaccine. We will investigate 1) roles of glycoproteins, gE and gl in pathogenesis, and 2) VZV infection of T cells and innate host cell responses as critical interactions preceding adaptive immunity. VZV gE and gl are predicted to be multi-functional proteins critical for cell-cell spread, envelopment and possibly entry. Consequences of specific mutations in gE or gl for growth, gE and gl trafficking, virion envelopment and entry will be determined. rOka gE and gl mutants will be tested to establish functions of gE and gl required for infection of skin, T cells or DRG in vivo. These experiments provide the opportunity to show how gE and gl determine VZV virulence in human neurons, as well as skin and T cells in vivo. We will also assess whether cellular transactivators that influence gE expression are cell-type specific determinants of VZV virulence. The SCIDhu skin model will be used to address questions about humoral immunity, determining if anti-glycoprotein antibodies affect VZV cell-cell spread in vivo or interfere with transfer from T cells to skin. In Aim 2, our model is that T cells transport virus to skin where VZV must overcome innate cellular barriers, enhanced by natural killer (NK) cells. We will examine interferon (IFN-alpha) and the expression of the toll-like receptor 9 in SCIDhu mice with VZV-infected skin xenografts and in vitro, to provide new information about innate cellular defenses against VZV. The effect of NK cells, which release IFN-gamma and tumor necrosis factors (TNF), on expression of adhesion molecules, chemoattractants, and VZV replication will be examined in skin xenografts. Finally, whether VZV-infected T cells transfer VZV to DRG as well as skin, will be examined using parent Oka and vaccine Oka viruses. Better understanding of the mechanisms of VZV tropism for T cells, skin and neural cells, and of innate antiviral immunity, will be useful for improving strategies to prevent varicella and zoster in healthy and immunocompromised individuals.